Pneumatic tires are sometimes constructed with a circumferential belt reinforcement positioned in their crown portion between tread and carcass. Such construction is often used with radial ply carcass tires and sometimes with bias ply tires.
The belt is typically a fabric-reinforced rubber in the form of a rubber encapsulated textile fabric, or multiple filament, such as steel, glass, nylon, aramid or polyester.
The belt reinforcement is used, for example, to control or limit the outward expansion or deformation of the tire in service, to provide some stability for the overall tire construction and to aid in providing a strengthening interface between the carcass plies and tread rubber.
Another and important purpose is to limit the distortion, or squirming, of the tread element as the tire rotates across a substrate (the ground or pavement, for example) and the tread passes through its footprint against the substrate. At this point of contact, a considerable and continuing flexing and distortion of the tire is observed in the region of the footprint. Belt reinforcement resists such distortion at the footprint which usually results in better tread wear characteristics.
High performance tires typically also have one or more overlay layers which are positioned between the belt reinforcement and the tread. Such overlay layers can be made utilizing a wide variety of materials with nylon being among the most common. Such overlay layers improve the tire's performance characteristics but are expensive to apply and add significantly to the cost of the tire.